This invention relates to controlling particulate contamination on surfaces of products, machine tools, and work areas. More particularly, the invention relates to measuring the removable particulate contamination on surfaces in semiconductor manufacturing, data storage manufacturing, fluid filter inspection, display manufacturing, clean rooms, pharmaceutical manufacturing and handling, precision mechanical manufacturing, optics manufacturing, aerospace manufacturing, and health care industries.
Quantified measurements of particulate contamination can comprise a total number of particles detected on the inspected surface, a total number of particles per area of the inspected surface, a size histogram of the total number of particles detected per area of the inspected surface, a cumulative particulate volume or area, or a combination of these measurements. Surface particle contamination measurements are generally performed by light scattering or image analysis.
U.S. Pat. Nos. 4,898,471 and 5,343,290 describe surface particle contamination measurements optimized for inspecting semiconductor wafers.
U.S. Pat. No. 4,766,324 describes comparing two scans of the same monitor wafer to determine particles added to or removed from the wafer between the two scans.
This invention also relates to removing particulates from surfaces. More particularly, the invention relates to cleaning processes to remove particulate contamination which are used in manufacturing systems to prevent localized defects, to prevent optical or beam scattering, prevent cross contamination of processing materials, to allow close mating of surfaces, to remove magnetic contaminants, and to sanitize surfaces. Surface particle removal is generally performed with the use of solvents, fluid shear, ultrasonics, transfer to a tacky surface, or mechanical agitation.
U.S. Pat. No. 4,009,047 describes contacting a sheet to be cleaned with a tacky roller.
U.S. Pat. No. 4,705,388 describes determining when a web-cleaning tack roller requires rejuvenation by measuring the optical reflectivity of the roller.
U.S. Pat. No. 5,373,365 describes measuring the reflectivity of a web-cleaning roller, and from that inferring the contamination level on the roller.
U.S. Pat. No. 5,671,119 describes cleaning an electrostatic chuck in a semiconductor process tool by adhering and removing a dummy tacky wafer to the chuck.
U.S. Pat. No. 5,902,678 describes cleaning a surface by applying an anti-static pressure sensitive film to a surface, irradiating the film with ultraviolet light, and removing the film.
U.S. Pat. No. 6,023,597 describes a method for forming a conformable anti-static roller.
Teknek Electronics Limited of Inchinnan, Scotland, makes printed circuit board cleaning products that first contact the circuit board with a conformal rubber roller, and then contact the rubber roller with an adhesive coated roller.
This invention further relates to combining cleaning a surface and to measuring the removable particulates on that surface. Combining these processes is useful for inspecting surfaces that are otherwise difficult to inspect by currently available techniques because the surfaces are too rough, optically scattering, or large. They are also useful because they combine a cleaning process that adds value to a product with a measurement that improves the control of the process.
U.S. Pat. No. 5,253,538 is embodied in the product QIII(copyright) available from Pentagon Technologies of Freemont, Calif. It describes inspecting a planar surface for particulates by shearing gas across the surface using a nozzle assembly, and subsequently inspecting that gas using an airborne particle counter.
U.S. Pat. No. 5,939,647 describes a system similar to a QIII for planar surface inspection in which the sampling head is attached to a handle by a gimbal.
U.S. Pat. No. 6,269,703 describes releasing particles from a surface using a fluid applied to shear across the surface. The fluid is then inspected for particulates.
The Surfex product from Particle Measuring Systems of Boulder, Colo., inspects surfaces by ultrasonic cleaning in an aqueous bath followed by inspection of the water by a liquid particle counter.
This invention further relates to retaining particulates removed from a surface on a carrier, determining the locations of the particles on the carrier, and passing the carrier and the locations of the particles on the carrier to other analytical instruments like electron microscopes, optical review stations, and x-ray absorption. Retaining the found particles gives tracability to the measurement technique. It allows follow up analysis to be performed on archived carriers to analyze product failure mechanisms and process changes.
U.S. Pat. No. 5,655,029 describes detecting a region of interest on a specimen with one microscope and conveying the specimen and the coordinates to a second microscope for automated review.
It would be desirable to provide a combination of surface particulate removal and particle measurement that would not scuff, abrade, or otherwise interact with the surface to generate more contamination. It would be desirable that the technique would not require the immersion of the surface in a solvent, allowing inspection of large, or vertically oriented, or solvent sensitive surfaces. It would be desirable that the technique would clean and inspect complex, rough, or non-planar surfaces. It would be desirable that the technique would inspect and clean interior surface of manufacturing tools with limited or confined access. It would be desirable that particulates that have been removed and detected from a surface would subsequently be analyzable by alternative analytical instruments.
This invention is a method and an apparatus that detects removable particulates initially on a test surface or a surface to be inspected. The removable particles are transferred to a portion of a tacky surface on a carrier by adhering and then removing the portion of the tacky surface from the test surface. The carrier is received by a positioning means and passed through the field of view of a surface inspection means guided by a controller. Signals from the surface inspection means are combined with coordinates from the controller to produce particle coordinates, which indicate particulates initially on the test surface. Particle coordinates on the tacky surface measured before the tacky surface is adhered and removed from the test surface can be compared with particle coordinates measured after the tacky surface is adhered and removed from the test surface. Several test surfaces can be sequentially inspected using the same carrier by storing particle coordinates after each measurement and comparing the most recent measurement with the cumulative previous measurements. The carrier and the associated particle coordinates can be conveyed to other analytical instruments for subsequent analysis.